1. Field of the Invention
The present invention generally relates to a material testing machine, in particular, to a material testing mechanism using a motor as a driving source of a loading mechanism.
2. Description of Related Art
A material testing machine using a motor as a driving source of a loading mechanism usually adopts the following structure, that is, two screw rods are supported on a table in this manner of being rotated freely, and two ends of a cross head are supported on each screw rod by means of nuts. The material testing mechanism is configured through the following manner, that is, each screw rod is made to rotate as the motor rotates, so as to make the cross head move, thereby applying a load to a test piece, and at this time, two ends of the test piece are held by chucks installed on the cross head and the table respectively.
In the material testing machine, a servomotor is generally used as the motor for driving the loading mechanism, and a test force applied to the test piece or an elongation of the test piece or the like is selected as a control quantity, and an instant inspection value of a physical quantity of the control quality is fed back to a target value, so as to control the motor (for example, with reference to Patent Document 1).
For example, under a situation of selecting the test force as the control quantity, a proportional integration differential (PID) and other operations are performed on the deviation between the inspection value (current value) and the target value, and a value corresponding to the result of the above operation is taken as a rotation angle command and sent to a servo amplifier, which supplies a driving signal to the motor used for driving, so as to control the motor.
Particularly, the rotation angle command is determined by combining constant times (proportional gain) of the deviation, constant times (derivative gain) of the time differential of the deviation, with constant times (integral gain) of the time integration of the deviation.
[Patent Document 1] Japanese Patent Laid-Open Publication NO. 2002-365188
However, in the material testing machine using the motor as the driving source of the loading mechanism, although the material test for tracking accurate target values can be performed accurately by appropriately setting the proportional gain, derivative gain, and integral gain, generally, in the system (sometimes including the test piece) each gain is actually set through trial and error.
Therefore, especially when testing a new type of test pieces, not only the corresponding time is required, but also skilled operators are required when each gain is set. However, it still cannot ensure that the test is performed accurately.